Our long term objective is to characterize the morphological and biochemical diversity of retinal ganglion cells (RGCS), and to determine the central projections of individual types of ganglion cells. RGCs differ not only in morphology and central projections, but also in: a) the input they receive and hence the content of receptor molecules for various putative transmitters; b) second messengers; c) the nature and number of various putative transmitters and "neuromodulators" presumably released at their central targets; d) response to injury; and e) their selective ability to regenerate. Our immediate specific aims include: 1) Continue ongoing efforts to identify putative transmitters and neuropeptides in RGCS, and define their unique central projections. We presently are concentrating on the neuropeptides enkephalin and cholecystokinin. 2) Identify receptors for transmitters and trophic factors in different populations of ganglion cells, particularly nicotinic acetylcholine, GABA(A) and NGF receptors. 3) Attempt to clarify the role of transport of nAChR receptor molecules in ganglion cell axons to "nonsynaptic" sites in the optic tectum (so-called "spurious transport"). 4) Determine temporal patterns of expression of transmitters and receptors in retinal neurons during embryogenesis. These studies may help identify factors regulating ganglion cell transmitters, growth and response to injury, as in trauma and glaucoma. Methods: light and electron microscopic immunohistochemistry, in situ hybridization, anterograde and retrograde pathway tracing methods. Animals: Pigeons, chick embryos, frogs.